I have a TH400 behind my Ls1 in my S10. It won't shift into 3rd unless the RPMs get above 4k. So to get into 3rd I have to go full throttle and then let off. Also while driving around my RPMs are really high, this might just be cause by the fact that it is a 3 speed but I'm not sure. Another thing is does anyone know a good brand for gear vendors, looking into a set but not sure what I should get.

 

could be vacuum related? dont the 400 use a vacuum signal like the 350s do?

 

yea I checked all the vacuum lines so I'm not sure.

 

The vaccuum source must be full and constant whenever the engine is running.Check this.The governor may have the wrong combination of weight and spring for your engine/ axle ratio combination.The shift valve springs in the valve body(there are inner and outers on the type 2 vb)can be in the wrong position causing this as well.